Recently, a magneto-optical recording medium has been widely utilized for applications such as a large capacity data file, in the form of a magneto-optical disk capable of writing and reading using laser light.
The magneto-optical recording medium has layers of a multilayer structure composed of an enhancing layer, a recording layer, a protective layer, an adhesive layer, etc., each having a thickness of from several tens angstroms (.ANG.) to several tens micrometers (.mu.m) formed on a transparent base plate such as, for example, a glass sheet, a plastic film, or the like, by a sputtering and other methods.
To produce a magneto-optical effect in the aforesaid recording layer, a single layer of an alloy of a rare earth metal and a transition metal or alternately laminated two or more layers of a thin film of the rare earth metal and a thin film of the transition metal each having a thickness of from several angstroms (.ANG.) to ten and several angstroms (.ANG.) are used. In particular, the latter type recording layer composed of the alternately laminated thin films of the rare earth metal and the transition metal produces excellent magnetization amount, coercive force and magneto-optical effect (Kerr effect) and has the advantage of easily controlled characteristics. Magneto-optical recording media having such a recording layer are disclosed in JP-A-61-108112, JP-A-59-217247, JP-A-62-26659, JP-A-62-71041, and JP-A-62-137753 (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application").
In particular, a magneto-optical recording medium having a recording layer composed of alternately laminated thin films of terbium (Tb) and an Fe-Co alloy shows the most excellent characteristics. However, Tb is an expensive material, which makes the widespread use of this material in a magneto-optical recording medium difficult. Thus, a magneto-optical recording medium wherein a part of Tb is replaced with inexpensive dysprosium (Dy) or gadolinium (Gd) to form a recording layer composed of the alternately laminated thin films of a Tb-Dy alloy and an Fe-Co alloy is proposed as disclosed in U.S. Pat. No. 4,727,005, JP-A-59-217249, etc. However, in the magneto-optical recording medium, a Kerr rotation angle (.theta..sub.k) does not become large and thereby the recording medium having a high C/N ratio is difficultly obtained. Also, in the case of using Gd as a part of Tb for a recording layer, the Kerr rotation angle (.theta..sub.k) may be increased but Hc becomes low and hence a magneto-optical medium having a high C/N ratio is not obtained.